This application claims the priority of Japanese Patent Application No. 12121/1994 filed Jan. 7, 1994, which is incorporated herein by reference.
This invention relates to a method and an apparatus of mounting a lens on a semiconductor light emitting device which is used as a light source in optoelectronic communications. Laser diodes and light emitting diodes are typical semiconductor light emitting devices. From the standpoint of material of substrate, the semiconductor devices are classified into a GaAs type, a GaP type, or an InP type. These semiconductor devices emit light beams with different wavelengths, because each material has a different inherent band gaps. The light emitting devices are also classified into two types by the configuration of emitting light beams. One is a surface-emission type which emits light perpendicular to a surface of films or a substrate. The other is a side emission type which propagates light in a waveguide parallel with a surface and emits light from a side end.
This invention alms at an improvement of the surface-emission type of light emitting device. Surface-emission type devices emanate light beams perpendicular to an interface of layered films (pn junction). Some emit light beams from a film surface. Others emit light from a substrate surface. In order to distinguish two types, the device emanating from the film surface is temporarily called a front surface emission type and the other device emitting from the substrate surface is now called a rear surface emission type. Light beams diverge in all directions from a narrow active region without being guided by a waveguide. Strong divergence of beams allows little part of the beams to enter an end of an optical fiber. Thus most of the surface emission type devices employ a lens for converging light beams and for introducing the beams into a core of a fiber.
Optoelectronic communications or optoelectronic measurements require small cores in fibers, because single-mode waves are preferable for transmitting a signal for a long distance without deformation or transmitting only one mode of signal. Prior devices have adopting ball lenses for gathering beams efficiently. A ball hens is favored with the shortness of a focal distance and isotropy. The short focal length effectively gathers light beams. Geometric isotropy facilitates the mount of a lens on a semiconductor device. Ball lenses are directly fixed on a light emitting device without space. The short focal length forbids the ball lens separating from the light emitting device. A lens has been fixed directly on a device. The surface-emission type installs a ball lens directly on a chip of a device without space or any spacer for gathering light beams effectively. The mount of a lens does not mean such an indirect coupling of bonding a chip on a package and encapsulating the package with a cylindrical cap having a lens at a window. Such a package and a lens-cap may be employed to seal the device at a later stage in order to fabricate double lens devices. The lens mount of this invention relates only to the direct coupling of a lens to a chip.